RELATED APPLICATIONS AND CLAIM OF PRIORITY

[0001] This application claims priority to U.S. provisional Patent Application No. 61/770,419, filed February 28, 2013, titled "CVI BONDED AND COATED PCBN TO WC TOOL BODY".

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY

[0002] The present invention relates to a cutting tool for metal machining, comprising at least one body containing polycrystalline cubic boron nitride (PCBN), with or without cemented carbide backing, and on the surface of said body a hard and wear resistant refractory coating, more specifically, to a method of using chemical vapor infiltration (CVI) or chemical vapor deposition (CVD) with porous or fine granule media to fill gaps between a PCBN tool tip and a WC tool body.

[0003] Polycrystalline cubic boron nitride (PCBN), polycrystalline diamond and polycrystalline diamond composite materials are commonly used to provide a superhard cutting edge for cutting tools such as those used in metal machining.

[0004] Cutting tools having cutting edges formed of a superhard abrasive such as a cubic boron nitride (CBN) based material are manufactured by powder

metallurgical techniques and are mainly used for the machining of cast iron and hardened steel. Several types of CBN cutting tools are known, the majority consisting of a PCBN tip that has been brazed onto a cemented carbide insert.

Others have the PCBN sintered directly to a cemented carbide backing of sufficient

1

INCORPORATED BY REFERENCE (RULE 20.6) thickness to produce an insert while yet others consist of a PCBN-containing body without any cemented carbide backing.

[0005] Subjecting a sintered PCBN body to temperatures over 1000 °C may result in unwanted structural changes in the material. Furthermore, in the case of a brazed insert, the braze joint will be destroyed.

[0006] Therefore, it can be seen that there is a need for a cutting tool having a high temperature bond between the PcBN tool tip and the tool body (WC/Co).

SUMMARY

[0007] In one embodiment, a cutting tool may comprise a sintered superabrasive tip having a plurality of superhard particles; a tool body retaining the superabrasive tip; and a non-brazing material filling gaps between the superabrasive tip and the tool body.

[0008] In another embodiment, a method may comprise steps of providing a sintered superabrasive tip; providing a tool body; filling a gap between the

superabrasive tip and the tool body with a non-brazing material; and depositing a first coating to the non-brazing material, wherein the first coating is an infiltrant coating to bond the tip, body and non-brazing materials to each other.

[0009] In yet another embodiment, a cutting tool may comprise a sintered

superabrasive tip having a plurality of superhard particles; a tool body retaining the superabrasive tip; infiltrant bond coating between the superabrasive tip and the tool body; and high temperature coatings attached to the sintered superabrasive tip and the tool body.

2

INCORPORATED BY REFERENCE (RULE 20.6) BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The foregoing summary, as well as the following detailed description of the embodiments, will be better understood when read in conjunction with the appended drawings. It should be understood that the embodiments depicted are not limited to the precise arrangements and instrumentalities shown.

[0011] FIG. 1 is a perspective view of a superabrasive tip affixed to a tool body according to an exemplary embodiment;

[0012] FIG. 2 is an optical image of a cross-sectional view of a superabrasive tip affixed to a tool body according to another exemplary embodiment;

[0013] FIG. 3 is a partially enlarged optical image of the cross-sectional view of a superabrasive tip affixed to a tool body as shown in FIG. 2; and

[0014] FIG. 4 is a flowchart illustrating a method of making a superabrasive tip affixed to the tool body according to an exemplary embodiment.

DETAILED DESCRIPTION

[0015] As used herein, the term "cutting tip" refers to a body for grinding or cutting a work piece, which is manufactured by fabrication processes including the step of mixing the super abrasive particles with bond.

[0016] As used herein, the term "tool body" refers to a rigid body that holds a cutting tip or tips firmly in place so that they can be utilized in a turning, milling, boring, cutting, or drilling application.

[0017] In an exemplary embodiment, a cutting tip may be made of superabrasive particles affixed to a suitable tool body, such as, cemented carbide hard metal. The exemplary embodiments use chemical vapor infiltration (CVI) or chemical vapor deposition (CVD) with porous or fine granule media to fill gaps between the superabrasive tool tip and a tool body. The deposition by CVI or CVD may bond the

3

INCORPORATED BY REFERENCE (RULE 20.6) porous or fine granule media to each other and to the cutting tip and the tool body. A high temperature resistant coating or sequence of multilayered coatings, such as Al ₂ 0 ₃ may be subsequently coated as a part of the same process to provide an enhanced wear resistance.

[0018] More specifically, the porous or fine granule media used may survive the CVI or CVD process. Alternatively, fine granule, such as diamond or cubic boron nitride, may be consumed by the process. A high temperature resistant coating or sequence of multilayered coatings may be deposited for providing additional wear resistance to the cutting tool during machining, which may not have effects on the strength of the bonding already established (unlike a metallic braze).

[0019] As shown in FIG. 1 , a cutting tool 10 may include a sintered superabrasive tip 12 and a tool body 14 that contains an aperture 19. The tool body 14 may be made from a number of materials, including cobalt cemented tungsten carbide. The tool body 14 may be designed to retain the superabrasive tip 12. The sintered superabrasive tip 12 may have a plurality of superhard particles, which may be selected from a group of cubic boron nitride, diamond, diamond composite, and ceramic materials. Between the superabrasive tip and the tool body may exist a seam or a gap, such as a bottom gap 15 and a sidewall gap 16, for example. The superabrasive tip 12 may or may not have a backing support. The backing support may be a hard metal support, such as a tungsten carbide support.

[0020] As shown in FIG. 2, the cutting tool 10 may comprise a superabrasive tip 12 having a tungsten carbide support 20. The superabrasive tip 12 may have polycrystalline cubic boron nitride (PcBN) particles. The cutting tool 10 may further include a tool body 14 retaining the superabrasive tip 12. A non-brazing material 24, which may have melting point at least 1000 °C, may be deposited to fill the sidewall gap 16 and the bottom gap 15. The non-brazing material 24 may be at least one of zeolite, ceramic, cubic boron nitride, and diamond, for example. The cutting tool 10 may further comprise coatings, such as infiltrant bond coating 22 on the non-brazing material 24 between the superabrasive tip and the tool body. The infiltrant bond

4

INCORPORATED BY REFERENCE (RULE 20.6) coatings 22 may cover the sintered superabrasive tip 12, the backing support 20, and tool body 14. The infiltrant bond coatings may comprise at least one of Group IVB compounds containing C, N, 0, B, such as TiN, TiC, and TiCN, ZrN, ZrC, ZrCN, HfN, HfC, HfCN, for example.

[0021] A close-up optical image shown in FIG. 3, illustrates that the coatings 22, such as TiN, may cover all cubic boron nitride crystals 24. The coatings 22 may further provide bonding between the non-brazing material, such as cBN, diamond, or zeolite, superabrasive tip 20, and the tool body 14.

[0022] Since the non-brazing material has melting point at least 1000 °C, a high temperature resistant coating, such as Al ₂ 0 ₃ (not shown) may be deposited or coated to the sintered superabrasive tip 12, the tool body 14, and non-brazing material disposed between the superabrasive tip 12 and the tool body 24.

[0023] FIG. 4 shows an exemplary method 400 of a process of fabricating a cutting tool. The process includes steps of providing a superabrasive tip in a step 401 ; providing a tool body in a step 402; filling a gap between the superabrasive tip and the tool body with a non-brazing material in a step 403; and depositing a first coating to the non-brazing material in a step 404.

[0024] The sintered superabrasive tip may be attached by some method to the tool body. The cutting tool may then be placed in a CVD (chemical vapor deposition) reaction vessel, whereupon air is removed and replaced by gases comprising both inert and reactive species. Metallic deposition may employ gases comprising metal carbonyl or metal- acetal-acetonates, for example, iron pentacarbonyl. Ceramic deposition precursors may refer to N, C, and 0 containing compounds that crack under temperature less than 1000 °C. In some exemplary embodiments, the ceramic deposition precursors may include TiCI ₄ , NH ₃ , CH ₄ , AICI ₃ , (Me) ₃ AI, N ₂ , CH ₃ CN, H ₂ , CO, C0 ₂ or mixtures thereof, for example. The gases penetrate via diffusion into gaps, seams, contact voids, and deposit on heated solid surfaces, external or internally gas- accessible, in the equipment. Upon condensation on the surface, the condensed phases chemically react to form a new solid phase as a first

5

INCORPORATED BY REFERENCE (RULE 20.6) coating. The first coating may be an infiltrant coating to bond the superabrasive tip, the tool body, and non-brazing materials together. For example, TiCI ₄ + CH ₄ -> TiC solid + gas phase 4HCI. This solid phase adhesively bonds to the solid surfaces depending on chemical affinity. The quality of the solid phase (crystal perfection, density) depends on temperature and affinity to the solid surface(s) upon which they condense. The process of infiltration, condensation and reaction to form a new solid phase continues as long as temperature is high enough and reactants are present. Once the pores are filled, then straight-forward coating on surfaces of the superabrasive tip and the tool holding material may occur.

[0025] Gas accessibility is determined by the gas diffusion, which depends on temperature and pressure. Lower pressure allows deeper diffusion of reactive gases into seams and gaps in the tool assembly. Gas deposition, reaction and solidification rates forming a solid must be controlled to prevent premature '"plugging" of narrow gaps and seams, thus reducing the film contact area and joint strength. This typically requires that the temperature be lowered, or gas phase partial pressure of reactants be adjusted. Finally, the quality of the film formed, its crystallinity and crystal orientation, depends on temperature and time. If the film is formed and quenched too quickly, it may be of poor quality and crack either within the film or at the film-tip or film-tool interface.

[0026] It is important that the gas-phase precursors react with solid surfaces indiscriminately, regardless of orientation in the reactor. So-called "line-of-sight" deposition processes, e.g., physical vapor deposition (PVD), may not be as effective as the gas-phase precursors, and may not penetrate gaps and seams, thus reducing the area of adhesion and adhesion strength considerably.

[0027] Furthermore, non line-of-sight CVD coating does not require tools to be flipped over and processed multiple times to form a uniform coating. CVD coats all gas-accessible surfaces in one furnace cycle.

[0028] Gas phase reactions that may also be considered CVD include any gas- solid reactions such as oxidation, hydration, or carburization. The solid constituents

6

INCORPORATED BY REFERENCE (RULE 20.6) may adsorb onto surfaces first, then react and crystallize, or may form above the surface and deposit by solid-surface tension forces prior to reaction and crystallization.

[0029] Post-CVD treatment, e.g., annealing may be conducted to improve the quality of the film or film-tip/film-tool adhesion.

[0030] One or more steps may be inserted in between or substituted for each of the foregoing steps 401-404 without departing from the scope of this disclosure.

[0031] While reference has been made to specific embodiments, it is apparent that other embodiments and variations can be devised by others skilled in the art without departing from their spirit and scope. The appended claims are intended to be construed to include all such embodiments and equivalent variations.

7

INCORPORATED BY REFERENCE (RULE 20.6)